An expandable well screen is disclosed in applicant's co-pending U.S. patent application Ser. No. 08/745,391, filed on Nov. 8, 1996, now U.S. Pat. No. 5,901,789, which is incorporated herein by reference PCT/EP96/04887, which has issued as U.S. Pat. No. 5,901,789 and which is incorporated herein by reference.
FIG. 3 of this prior art reference discloses that the filter sheets consist of plates in which a series of circular perforations are present. The size of these perforations is chosen such that solid particles larger than the size of the hole are prevented from flowing into the well.
A suitable expandable slotted carrier tube for use with the screen is disclosed in U.S. patent application Ser. No. 72,290, filed on Jun. 7, 1993, now U.S. Pat. No. 5,366,012, which is incorporated herein by reference. PCT/EP93/01460, which has issued as U.S. Pat. No. 5,366,012, which is incorporated herein by reference.
It has been found that filter sheets which are secured to an expandable slotted carrier tube are deformed considerably during the process of expanding the carrier tube by moving an expansion mandrel therethrough. The carrier tube normally shortens during the expansion process as a result of opening of the axial slots towards a diamond shape.
This may cause the filter sheets to buckle to accommodate the carrier tube shortening and friction between the overlapping filter sheets and the carrier tube or tubes may cause the filter sheets to tear.
An object of the present invention is to provide a well screen comprising an iris-shaped configuration of filter sheets which do not buckle and which slide easily relative to each other and relative to the carrier tube during the process of expanding the carrier tube.